The symmetric hexachlorobiphenyls (HCB) 2,4,6,2',4',6'-HCB, 2,3,6,2',3',6'-HCB, 2,4,5,2',4',5'-HCB, 2,3,4,2',3',4'-HCB and 3,4,5,3',4',5'-HCB were fed to chicks and the excreta collected and extracted. The metabolites isolated were identified by gas chromatography-mass spectrometry (GCMS). No metabolites were found for the 3,4,5,3',4',5'-HCB or the 2,3,4,2',3',4'-HCB. One hydroxy metabolite was found for the 2,3,6,2',3',6'-HCB but not in sufficient quantity to allow further characterization. The 2,4,6,2',4',6'-HCB was found to be metabolized to a methylpentachlorobipheynl, a methylhexachlorobiphenyl, 2,4,6,2',3',4'-HCB and a pentachlorobiphenyl. The 2,4,5,2',4',5'-HCB was found to be metabolized to 3 hydroxy 2,4,5,2',4',5'-HCB, a hexachlorobiphenylquinone and a pentachlorobiphenylquinone. The latter two were probably formed from the corresponding dihydroxyl compounds during sample work-up.